Fe³⁺/ΣFe variation in lawsonite and epidote in subducted oceanic crust

Titelangaben

Whitney, Donna L. ; Wilke, Max ; Hanel, Sara E. ; Heidelbach, Florian ; Mathon, Olivier ; Rosa, Angelika D.:
Fe³⁺/ΣFe variation in lawsonite and epidote in subducted oceanic crust.
In: European Journal of Mineralogy. Bd. 37 (2025) Heft 2 . - S. 143-149.
ISSN 1617-4011
DOI: https://doi.org/10.5194/ejm-37-143-2025

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Abstract

The hydrous Ca–Al silicates lawsonite and epidote group minerals (EGMs) are key phases in subduction-zone H2O and element cycling. In high-pressure–low-temperature metamorphic rocks, Fe in both minerals is typically assumed to be entirely Fe3+, which substitutes for Al in octahedral sites as a major component in most EGMs and as a minor component in lawsonite and zoisite. New Fe micro-X-ray absorption near-edge spectroscopy (μ-XANES) analyses show substantial Fe2+ in lawsonite in blueschist from New Caledonia and zoisite from an unknown locality. Analysed Fe-rich EGMs (epidote, clinozoisite) contain primarily Fe3+. Lawsonite and some EGMs in subducted oceanic crust may contain more Fe2+ than is currently known, with possible implications for understanding subduction redox processes and conditions and why they vary in different subduction zones.